HTML validator technically refers to validation using DTDs by SGML tools. Use of the term refers to checking an HTML document for various problems using some type of computerized checker, and not necessarily by using a DTD with SGML tools.

Is there anything apart form W3Cvalidator to validate websites? If yes, then share here until now I am also using the same validator, but my friend was asking about some other validator, which he also does not remember.

There are some other tools as well, which help in html validation. Try using some here http://bit.ly/13RVUwY

HTML validator checks to make sure the HTML code on your web page complies with the standards set by the W3 Consortium, the organisation that issues the HTML standards. There are various types of HTML validators: some only check for errors, while others also make suggestions about your code, telling you when it might lead to (say) unexpected results.